A Static Nonlinear Procedure for the Evaluation of the Elastic Buckling of Anchored Steel Tanks Due to Earthquakes

Ground-supported steel tanks experienced extensive damage in past earthquakes. The failure of tanks in earthquakes may cause severe environmental damage and economic losses. This study deals with the evaluation of the elastic buckling of above-ground steel tanks anchored to the foundation due to seismic shaking. The proposed nonlinear static procedure is based on the capacity spectrum method (CSM) utilized for the seismic evaluation of buildings. Different from the standard CSM, the results are not the base shear and the maximum displacement of a characteristic point of the structure but the minimum value of the horizontal peak ground acceleration (PGA) that produces buckling in the tank shell. Three detailed finite element models of tank-liquid systems with height to diameter ratios H/D of 0.40, 0.63, and 0.95 are used to verify the methodology. The 1997 UBC design spectrum and response spectra of records of the 1986 El Salvador and 1966 Parkfield earthquakes are used as seismic demand. The estimates of the PGA for the occurrence of first elastic buckling obtained with the proposed nonlinear static procedure were quite accurate compared with those calculated with more elaborate dynamic buckling studies. For all the cases considered, the proposed methodology yielded slightly smaller values of the critical PGA for the first elastic buckling compared to the dynamic buckling results.     

Earthquake Faulting Effects on Buried Pipelines – Case History and Centrifuge Study

Permanent ground deformation (PGD) is one of the most damaging hazards for continuous buried lifelines. This hazard is especially severe when the PGD results in net compression in the pipe. In that case, buckling of pipe material can occur. If buckling is moderate, deformation of the pipe cross-section can lead to flow restriction and high friction losses, and eventually require line replacement. If buckling is severe, high localized strains can lead to pipe rupture, loss of contents, and possible pollution of surrounding soil. In this article, centrifuge tests of buried pipelines subject to abrupt ground failure in the form of surface faulting are presented. The fault movement results in mostly compression in the pipe. The test results are compared with a case history of pipe failure in the 1999 Izmit, Turkey earthquake and also with the results from the centrifuge tests which result in net tension in the pipe. The experimental setup, procedures, and instrumentation are described in detail. Suggestions for design practice are offered based on the analysis of results from both the 1999 Izmit case history and the centrifuge modeling.     

Numerical Simulation and Seismic Fragility Analysis of a Self-Centering Steel MRF with Web Friction Devices

This article presents the seismic fragility analysis of a self-centering steel moment-resisting frame (SC-MRF) with web friction devices. A detailed numerical model of the SC frame was developed using the Open System for Earthquake Engineering Simulation (OpenSees) and the elastoplastic responses of the SC-MRF were studied, including the strength degradation under cyclic loading, tendon rupture, beam buckling, bolt bearing and friction loss, etc. The proposed simulation approach is validated by comparing the simulated results with those in existing hybrid-simulation tests, quasi-static pushover test and low cyclic tests, where good agreement is observed. In addition to the well-established performance limit states (i.e., immediate occupancy, collapse prevention and global dynamic instability), two unique performance limit states (i.e., the recentering and repairable limit states) are defined for the SC-MRF. Finally, incremental dynamic analyses are conducted to evaluate the seismic fragilities regarding the five performance limit states.     

商周时期圈足铜器的三角形加强筋技术浅析

商周时期青铜器上的三角形加强筋技术主要用于觚、尊、簋、卣、壶、瓿、盘等圈足器的底部与圈足连接处,纵向延伸,上端较粗,承接铜器外底,下端向下延伸逐渐变细,多为等距或对称分布。加强筋的大小、数量多少的设置,根据器形因器而异,铜觚器体修长,圈足较高,加强筋多为2条或4条,纵向延伸较长,而铜簋、方彝等,底部面积较大,圈足粗矮,加强筋数量相对较多,纵向延伸较短。三角形加强筋技术起源于商代早期郑州商城陶鼎、铜鼎鼎耳与口沿连接处采用的加强筋技术,商代晚期至西周早期比较盛行,延用至春秋早期。商代晚期圈足铜器上使用较多,但又不仅限于圈足器,部分带鋬器,如爵、斝等,鋬的两端与鋬下腹壁连接处也有发现。其功能在于防止铸件连接处因凝固收缩的应力作用而出现裂纹,强化圈足器器底与圈足之间连接。     

EXPERIMENTAL BEHAVIOUR AND NUMERICAL MODELLING OF SMOOTH STEEL BARS UNDER COMPRESSION

Many existing reinforced concrete buildings located in seismic regions are characterised by internal steel reinforcement made of smooth bars and stirrups with inadequate spacing. These bars could be subjected to significant compression and eventually buckle. This paper deals with a comprehensive experimental campaign investigating the compressive behaviour of smooth bars for different values of the ratio L/D, L being the restraints distance and D the bar diameter. The stress-strain relationship is then modelled ranging from an elastic-plastic behaviour identical to that in tension (L/D=5) to the elastic buckling behaviour (L/D>20). The comparison between the experimental results and the outcomes of the model confirms the accuracy of the proposed stress-strain relationship.     

Cyclic Behavior of Smooth Steel Reinforcing Bars: Experimental Analysis and Modeling Issues

This article presents the results of an experimental campaign on the cyclic behavior of smooth steel bars, used as internal reinforcement of existing Reinforced Concrete (RC) structures; the stress-strain relationship is analyzed for different values of L/D ratio, where L is the stirrup spacing and D is the longitudinal bar diameter. Most of the experimental tests concerned smooth bars with L/D ratios ranging between 5 and 100. The analysis of the test results is complemented by some comparisons of the curves obtained by experimental tests on smooth steel bars with those obtained by experimental tests on ribbed steel bars. The theoretical predictions obtained by existing models available in the literature on the cyclic behavior of ribbed steel bars are then discussed. Our review of these formulations underlines their range of applicability as well as their potential to predict the damage and buckling that occur for different L/D ratios of the smooth steel bars.     

The 19th-Century Suspension Footbridges of Harpers of Aberdeen

Abstract

Harpers of Aberdeen, Scotland, developed a light suspension footbridge that had little connection with the 'blacksmith bridges' of the earlier part of the 19th century. Apart from scale, they differed in having a unique tensioning device together with an arched deck. Of perhaps 60 built, only a handful survive. They have not previously been described. These bridges provide a valuable insight into the affordable and adaptable engineering solutions, easily exported to all corners of the empire, which were adopted for small-scale projects during the course of the 19th century.     

Eighteenth‐Century Meissen Porcelain Reference Data Obtained By Proton‐Beam Analysis (PIXE–PIGE)

Prior to their restoration, the porcelain bodies of broken pieces from 31 authentic Meissen objects of the early 18th century were investigated by proton‐beam analysis. Attention was paid so that the proton beam probed only the bare porcelain paste areas of fractures. Thus, contributions to the measured X‐ray and γ‐ray spectra from adjacent surface glaze were prevented. The chemical compositions, obtained by simultaneous detection of elements with Z ≥ 13 (X‐rays) and lighter elements Z ≤ 14 (γ‐rays), represent rather consistent mixtures of paste ingredients. This result highlights the durable recipes and raw materials used in early Meissen porcelain production in the years 1725–50. Mean concentration values of element oxides, deduced from the detailed measurements, prove suitable for use as a database for Meissen porcelain paste identification. Material authentication of intact objects, without access to the bare porcelain body, is demonstrated by inspection of the white glaze. Unique museum objects are examined in atmosphere and without sampling. A low proton‐beam intensity and a short irradiation time ensure non‐destructive analysis. Simultaneous radiation and backscattered particle detection allow complete composition analysis, using the established ion beam techniques of particle‐induced X‐ray emission (PIXE), particle‐induced gamma‐ray emission (PIGE) and Rutherford backscattering spectrometry (RBS).     

Effect of Cyclic Loading Frequency on the Behavior of External RC Beam-Column Connections

Reduced-scale external RC beam-column specimens with three typical deficiencies as beam weak in flexure (BWF), beam weak in shear (BWS) and column weak in shear (CWS) were tested under cyclic excitations of different frequencies, varying from 0.025–2.0 Hz. Parameters like load carrying capacity, stiffness degradation, energy dissipation, principal tensile stress were monitored for exploring the effect of rate of loading on different types of deficient beam-column connections in a holistic manner. Test results showed that the rate effect is significant in beam-column connection with BWF, while the same is not so significant in BWS and CWS specimens.     

THE COMMONPLACES OF “REVISION” AND THEIR IMPLICATIONS FOR HISTORIOGRAPHICAL UNDERSTANDING

Recognizing the contingent entanglement between historiography's social and political roles and the conception of the discipline as purely factual, this essay provides a detailed analysis of “revision” and its connection to “revisionism.” This analysis uses a philosophical approach that begins with the commonplaces of our understanding as expressed in dictionaries, which are compared and contrasted to display relevant confusions. The essay then turns to examining the questions posed by History and Theory's Call for Papers announcing its Theme Issue on Revision in History, and, where philosophically relevant, answers them. The issue of paradigm change proved to be quite significant and required particular attention. A “paradigm” is analyzed in terms of Quine's “web of belief,” and that web is itself explained as an ongoing process of revision, in analogy with Rawls's concept of pure procedural justice. Adopting this approach helps clarify the entanglement between politics and historiographical revision.     

宁波保国寺大殿北倾原因浅析

宁波保国寺是浙东现存最古老的宋代木结构建筑,自清乾隆时期起,大殿结构发生北倾,后对4号转角檐柱进行修缮并加固至今,通过跟踪测试没有发现新的倾斜趋势。然而,探讨大殿曾经北倾原因以及经修缮后现今大殿的可靠性无疑仍是必要的。古木结构的特点是梁柱的榫卯连接具有半刚性性质。采用有限单元法对大殿结构进行力学分析时,榫卯连接可采用空间二节点虚拟弹簧元进行模拟,单元刚度矩阵中相应的刚度特性系数可由接触有限单元法近似求得。这样,大殿结构可离散为杆、梁、壳、体元和上述虚拟弹簧元等的组合,在屋面荷载、雪荷载和风荷载作用下采用有限元法可求得各节点的位移和相应应力。通过计算表明,不计4号柱时产生的向北位移比考虑该柱参加受力时要大得多,可见北倾原因确系4号柱年久失效而引起。计算结果也表明,现今大殿结构由受力来看是安全的。同时预示了可能出现的最危险部位。保国寺大殿结构的力学分析结果,为物保护工作提供了科学依据。     

Increasing Seismic Energy Dissipation of Steel Moment Frames Using Reduced Web Section (RWS) Connection

Connections of steel moment frames are vulnerable to brittle failure. Providing a perforation near the beam-ends is suggested as a potential method to improve seismic behavior of these structures. This article presents a numerical study on the energy dissipation of steel moment connections with perforated beam. Models with elongated circular openings of different dimensions and location are analyzed and compared based on the global and local damage indices, predicted failure time and dissipated energy. Results show that an RWS connection with a proper opening size can develop reasonable inelastic deformations and provide an acceptable seismic improvement to moment-resisting frames.     

故宫中和殿某中金檩断裂分析

勘查发现,故宫中和殿明间某中金檩在与上部爬梁相交位置出现局部断裂,造成下部中金枋产生较大挠度.为探明该中金檩产生断裂的原因,采取理论计算与数值模拟相结合的方法,对中金檩、中金枋体系进行了分析.基于榫卯连接边界条件的特征,分别考虑中金檩与中金枋叠合、中金檩与中金枋分离、中金檩完全断裂等三种工况,建立了中金檩-枋体系的受力模型,进行了静力分析,获得了中金檩、中金枋的变形及内力分布特征,讨论了中金檩断裂破坏的影响因素.结果表明:由于中金檩在爬梁作用位置截面削弱,造成中金檩自身拉、压、弯承载力不足,从而导致中金檩产生断裂;中金檩与中金枋分离条件下,中金檩断裂造成的中金枋内力增加,且比檩枋叠合条件更明显;中金檩完全断裂后,将造成中金枋内力及变形剧增,威胁中金枋安全.因此,对中金檩采取及时有效的加固措施极其重要.研究结果将为中金枋采取加固措施提供理论参考.     

MOMENT RESISTING WELDED CONNECTIONS: AN EXTENSIVE REVIEW OF DESIGN PRACTICE AND EXPERIMENTAL RESEARCH IN USA,JAPAN AND EUROPE

Welded connections, widely used in seismic moment resisting frames (MRFs) in USA, Japan and Europe, have been extensively investigated during the 1990s in order to improve their performance under severe earthquakes. In order to correctly evaluate the results of experimental research on welded connections, the differences among the American, Japanese and European current practices in designing the frame structural systems and in detailing the beam-to-column connections should be firstly appraised. In this paper, the major aspects characterising the USA, Japan and Europe design practice in moment resisting welded connections are reported, the differences are underlined and the main issues recently addressed in experimental research are reviewed. Among the several parameters which affect the connection performance, attention is focused on the effect of the beam cross-section size. Thus conclusions are drawn in terms of plastic rotation capacity as dependant on the beam size.     

南方地区唐宋元时期滴水研究

长江流域以及广东地区等南方地区的衙署、寺庙、居址、城址、墓上建筑等遗址中出土了一定数量的唐宋元时期滴水,其中以峡江地区及长江下游地区分布较密集。出土滴水整体呈长条弧形和弧边三角形两种形状,大致可分为唐-五代时期和宋-元时期两个阶段。唐-五代时期主要流行长条形滴水,饰几何形图案;宋-元时期沿用长条形滴水的同时,主要流行弧边三角形滴水,纹饰图案较为丰富。对比宋金西夏时期北方地区的滴水,可知其时南北地区滴水呈现出鲜明的地方特色,尤其是纹饰相差较大;元代后趋于一致,历明清沿用至今。     

OUT-OF-PLANE SEISMIC RESISTANCE OF MASONRY WALLS

Seismic vulnerability of unreinforced masonry buildings is studied by means of simplified out-of-plane collapse mechanisms that take into account connections with transversal walls. According to experimental evidence, the analysis assumes that failure is reached with a rigid body motion of a part of the facade that falls down. Two classes of mechanism are examined: the overturning of the facade due either to a vertical crack at the connection or a diagonal crack on the transversal wall, both defined resorting to a simple model of masonry fabric, viewed as a regular assembly of rigid blocks and elastic plastic joints with friction but no cohesion. The use of simplified mechanisms give rise to an explicit evaluation of the seismic resistance to changes in the geometry and in the masonry fabrics, that could be used by practising engineers. This formulation is developed for both static horizontal actions and ground velocity peak, in the belief that the latter probably gives a better approximation of seismic action, while also providing, by comparison with the results of static forces, an estimate of the behaviour factor for unreinforced masonry. Eventually, the analytical forecasts are compared with numerical results obtained by means of the distinct element method.     

Displacement-Based Assessment of Non Ductile Exterior Wide Band Beam-Column Connections

Results from testing two half-scale exterior wide band beam-column sub-assemblages under cycles of lateral displacement are presented in this article. The first subassemblage represents the current level of detailing adopted in low to moderate seismic regions, such as Australia, for connections where seismic provisions are not normally a consideration in design. Minor (inexpensive) detailing changes in the reinforcement distribution and anchorage were introduced to the second test specimen. These changes significantly improved the connection performance in terms of increased displacement capacity and a reduction in strength deterioration. Using a displacement-based assessment approach to assess primary moment-resisting band beam frames of up to eight stories, it was found that the current level of detailing is adequate for the drift demands resulting from the expected Australian seismicity for a 500-year return period. However, for the displacement demands corresponding to a 2500-year return period, the frames sited on very soft soils and frames over four stories sited on intermediate soils would require improved detailing such as that used in the second sub-assemblage. A strength hierarchy of strong column-weak beam was assumed in this assessment.     

我国虚拟旅游网站的功能评价研究

随着虚拟现实技术的发展,越来越多的人开始享受虚拟旅游,虚拟旅游网站和其他网站的本质区别在于其所提供的虚拟旅游产品和服务,因此,虚拟旅游产品和服务的质量构成了网站的核心竞争力。本文选取具有代表性的虚拟旅游网站作为研究对象,在虚拟旅游和网站评价指标体系相关研究的基础上,建立虚拟旅游网站的评价指标体系,并采用内容分析法进行实证研究,以探究目前我国虚拟旅游网站的功能概况。研究结果显示:一方面,目前我国虚拟旅游网站界面功能结构不完整,主要表现为用户界面友好性低、更新不及时、交互性不强等问题。另一方面,就网站的虚拟旅游产品和服务而言,其内容较单调,对虚拟现实技术的应用不够深入,体验性设计不够,多数网站还处于对虚拟旅游产品和服务进行低水平开发的阶段。为此,笔者提出了相关建议,并对后续研究进行了展望。     

Stability of Slender Masonry Columns with Circular Cross-Section under Their Own Weight and Eccentric Vertical Load

This work concerns the stability of unreinforced masonry slender circular cross-sectional columns subjected to their own weight and eccentric vertical load. Cantilever columns are examined, considering that the material has infinitely linear elastic behavior in compression and has no tensile strength. For the analysis, an existing numerical model and solution procedure developed for the stability analysis of masonry elements with rectangular cross-section are utilized and adapted to the circular columns. For the instability of the columns, an appropriate criterion that relates the top lateral deflection to the intensity of the applied eccentric vertical load is employed. By considering a reference column, critical buckling load is obtained, behavior of the column interpreted and efficiency of the numerical model emphasized. Performing a nonlinear buckling analysis using a general purpose software on this reference column, obtained results are compared with those of the adapted procedure of the present study. Implementing parametric analyses on reference column, effects of the column slenderness, eccentricity of vertical load, elastic modulus, and self-weight on the buckling load are investigated. Presented calculation procedure provides a useful tool in order to calculate the critical loads or to check the stability of masonry circular columns.